Process of forging magnesium alloys



Patented Au .'4, 1931' UNITED STATES PATENT oFFice GILBERT MICHEL, OF BAGNE'UX, FRANCE, ASSIGNOR T SCCIETE LE MAGNTESIUM INDUSTRIEL, OF PARIS, FRANCE PROCESS OF FORGING MAGNESIUM ALLOYS No Drawing. Application filed March 24, 1828, Serial No. 264,578, and in France March 31, 1927.

My invention relates to a process for forging alloys having a magnesium base.

' In the manufacture of certain articles from magnesium, such as motor pistons, for example, it is necessary to make use of a1- loys possessing a good thermal conductivity and capable of being forged.

It has already been attempted to form industrial alloys of magnesium of good thermal conductivity by adding copper to this metal dustrial alloys of magnesium and copper that have been obtained have not been tapable of 5 being forged.

The object of my invention, therefore, is to add not over 6% (and preferably about 4%) of copper to the magnesium for giving- 4 thereto a higher thermal conductivity without destroying its forgeability. I

.The most useful alloys are those which are obtained by adding aluminium in the proportion of l to 5% to the co er-ma 'nesium al-' loy for increasing the hardness thereof.

My invention also embraces the addition of cadmium to the alloys above mentioned, for increasing their forgeability.

More specifically the invention concerns a process of forging alloys of magnesium such 5 as those above given, consisting in bringing the article to be forged up to 485 C. and maintaining it at that temperature before the forging operation takes place, until the very center of the said article is raised to this temperature and until the state vor molecular structure will be uniform throughout the whole mass.

By way of example, in no way of illustration, and without limiting the invention 40 thereto, the following example gives a quaternary alloy which has given particularly good results:

Parts Magnesium 93 Aluminium; 2 Copper 4 Cadmium 1 .50 ductivity and the metal remains forgeable.

in a substantial, proportion, for example. 10% or more; but up to the present the 111- If the proportion of copper is raised above 6% the metal becomes unforgeable.

If the copper-magnesium alloy were without other constituents, it would be too soft, the Brinell hardness being from about 48 to 49 according to the copper content.

The addition of aluminium has the effect of increasing the hardness. This addition must be made, according to the present invention, in the proportions of from 1 to 5% and preferably from 2 to 4%. In this way a hardness of from 58 to 62 is obtained.

It; has been proven that with over 5% aluminium, the ternary alloy magnesium-copper-aluminium becomes too brittle to be forged and employed industrially.

The addition of cadmium increases the forgeability of the alloys and prevents the usual constant formation of flaws in the metal during the forging operations. The invention, although it comprehends the addition of cadmium to all alloys of magnesium, is more especially applicable in the case of magnesium-copper alloys.

In this particular case it has been proven that the best results are obtained by adding the cadmium in the proportion of 0.2 to 1.5%. The proportion of 1% cadmium appears to be a good average.

Furthermore I may add manganese or cerium in the proportion of 0.2% to 1% for modifying the qualities of hardness of the metal or alloy at will.

Almost insurmountable difficulties are met in the forging of these alloys of a magnesium base containing 2 to 6% of copper, with or Without aluminium or cadmium, if certain precautions are not taken.

In accordance with the present invention, the critical temperature at which the forging is effected under the best conditions is 485 C. and care must be taken to maintain this temperature as close as possible, the permissible variation being 10 C. above or below, (i. e. between 475 and 495 (1.).

The best'results are obtained by progressively bringing the members or castings to be treated up to this temperature. I therefore preferably bring the members or castings up to a temperature of 250 to 300 C. and hold them there for several hours (for example, all night) with the temperature constant, after which I continue elevating the temperature up to 485 C. and when the entire mass of the member has been maintained at this temperature'for a sufficient length of time, depending upon the size of the said mass, I execute the forging operations to be performed. If. the operation cannot be performed in a suflieiently short time that the temperature can be considered constant during the duration thereof, the member must be subjected'to intermediate reheating for maintaining the temperature in the neighborhood of 486 C. It may frequently happen, during the fabrication of certain members of rough out form, that it be necessary to reheat several times.- 7

'i'he present invention further compre- :0 hends by way of new industrial products, ob-

jects of forged magnesium alloy, containing 2 to 6% copper and specifically forged quaternary alloys such as those above mentioned.

It is to be understood that the term forgusual forging operations and conducting the forging operations while at the'temperature of about 485 C. whereb the said member is given a uniform molecu ar structure.

2. The process of forging magnesium all6ys containing a small percentage of cadmium and containin less than 6% copper which comprises 'sub ecting the member to ing as herein employed is in a generic sense C. and 495 be forged to a temthe said temperature before performing the tions whereby the said member is given a uniform molecular structure, the aluminum in said alloy increasing the hardness thereof.

4. The process which comprises forging an alloy of a magnesium base containing less than 6% copper and less than 6% alummum, while the entire mass of alloy is between 475 and 495 C. v

5. The process which comprises forging an alloy of a magnesium base containing less than 6% copper and from 0.2 to 1.5% cadmium, while the entire mass of alloy is between 475 and 495 C.

6. A process which comprises forging an alloy containing magnesium as its principal constituent, about 2% aluminum, and containing no over 6% copper, and about 1% cadmium, while the Whole mass of said alloy under treatment is at between 471, C. and 495 C.

7. A process which comprises forging an alloy containing about 93% magnesium, about 2% aluminum and about 4%1 copper, and about 1% cadmium, While the whole mass of said alloy under treatment is at between 47 59 c. I z

GILBERT MICHEL,

be forged to a'temperature of 485 C. and

perature until the entire mass of the said member is raised to the said temperature before performing the usual forging operations whereby the said member is given a uniform 5.1 molecular structure, the cadmium in said maintaining the said member at the said tem- 

